An IP address duplication detection method is known by which duplication of IP addresses is detected by sending an ARP request to obtain a MAC address corresponding to the inputted IP address of the inspection object and determining the number of received ARP replies (see Japanese Patent No. 3534305).
An IP management method is also known that includes setting the sender address of the detected ARP packet as a protection IP, transmitting to the sender address an ARP packet that has been operated in the address that has already used the transmission IP address when the transmission MAC address is different from the designated MAC address, and transmitting a compensation packet to all of the devices on the network, wherein the compensation packet performs compensation such that the actually used MAC address of the transmission IP address becomes the designated MAC address (Japanese Translation of PCT Application No. 2008-520159).